Test of parallel alarm units

ABSTRACT

AN IMPROVED SIGNAL INSTALLATION OF A PLURALITY OF ALARM UNITS IS DISCLOSED, THE SIGNAL INSTALLATION ENABLING THE IPERATIONAL READINESS OF EACH ALARM UNTI TO BE CHECKED IN A SIMPLE AND RELIABLE MANNER. THE BASIC SIGNAL INSTALLATION ITSELF COMPRISES A PLURALITY OF INDIVIDUAL ALARM UNITS, EACH ALARM UNIT BEING CONNECTED IN PARALLEL PREFERABLY ACROSS A PAIR OF SUPPLY CONDUCTORS LEADING TO SOME CENTRAL MONITORING STATION. EACH ALARM UNIT IS PREFERABLY OF THE TYPE WHEREIN, AT THE OCCURRENCE OF AN ALARM CONDITION, AN ELECTRICAL CONTACT IS CLOSED THEREIN ESSENTIALLY SHORTING THE SUPPLY CONDUCTORS. FOR PURPOSES OF CHECKING THE OPERATIONAL READINESS OF THE PLURALITY OF ALARM UNITS, ALARM CONDITIONS ARE ELECTRICALLY SIMULTED AT EACH ALARM UNIT. WHEN EACH ALARM UNIT RESPONDS TO THE CHECKING OPERATION, AND ADDITIONAL ELECTRICAL CONTACT ASSOCIATED WITH EACH ALARM IS CLOSED. THE ADDITIONAL OR CHECKING ELECTRICAL CONTACTS ARE CONNECTED IN A SEPARATE SERIES CIRCUIT LEADING BACK TO THE CENTRAL MONITORING STATION. IF ALL ALARMS OF THE PLURALITY OF ALARM UNITS HAVE PROPERLY RESPONDED TO THE CHECKING OPERATION, THEN THE SEPARATE SERIES CIRCUIT COMPRISING ALL THE ADDITIONAL ELECTRICAL CONTACTS WILL BE COMPLETED. SHOULD ONE OF THE PLURALITY OF ALARM UNITS FAIL TO RESPOND, THEN ITS ASSOCIATED ADDITIONAL ELECTRICAL CONTACT WOULD REMAIN IN AN OPEN CONDITION THUS BREAKING THE SERIES CIRCUIT TRIGGERING AN INDICATOR AT THE CENTRAL STATION.

States Patent [72] Inventor Andreas Scheidweiler 3,447,145 5/1969Schumann 340/2131 pp NO a g g Primary Examiner-John W.Caldwelll Filed 18968 jssislant EismineriPerry Palan 4s Patented June 28, 1971 Mme) K [73]Assignee A.G. Cerberus 2 P r gg i s ABSTRACT: An improved signalinstallation ofa plurality of i d alarm units is disclosed, the signalinstallation enabling the :52 32? operational readiness of each alarmunit to be checked in a l I simple and reliable manner. The basic signalinstallation itself comprises a plurality ofindividual alarm units, eachalarm unit [54] TEST OF PARALLEL ALARM UNITS being connected in parallelpreferably across a pairof supply 7 Claims 3 Drawing Figs conductorsleading to some central mon toring station. Each alarm unit 15preferably of the type wherein, at the occurrence 1 1 Cl 340/410, of analarm condition, an electrical contact is closed therein 340/228essentially shorting the supply conductors. For purposes of [51] lnt.ClG08b 17/12, checking the operational readiness f the plurality f alarm00gb 29/00 units, alarm conditions are electrically simulated at each[50] Field of Search 340/213, alarm unit. w each alarm unit responds tothe checking 213.1, 214, 215, 227, 228, 228.1, 410, 411, 228.2, eration,and additional electrical contact associated with 408,409. 22 each alarmis closed. The additional or checking electrical contacts are connectedin a separate series circuit leading [56) References Cited back to thecentral monitoring station. If all alarms of the plu- UNITED STATESPATENTS rality of alarm units have properly responded to the checking2,847,662 8/1958 Lindgren 340/227.1 operation, then the separate seriescircuit comprising all the 3,235,858 2/1966 Mader 4. 340/214 additionalelectrical contacts will be completed. Should one of 3,530,450 9/1970Walthard et a1. 340/214 the plurality ofalarm units fail to respond,then its associated 2,639,418 5/1953 Sundstrom et al. 340/228 additionalelectrical contact would remain in an open condi- 2,895,'125 7/1959Watts 340/227 tion thus breaking the series circuit triggering anindicator at 3,128,457 4/1964 Culbertson 340/2131 the central station.

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INVENTOR ATTORNEYJ,

TIEST 01F PARALLEL AlLAlltll l UNl'll'S BACKGROUND OF THE INVENTION Thepresent invention generally relates to alarm signal installations andparticularly concerns an improved alarm signal installation of the typeincorporating a plurality of parallel connected individual alarm unitsalong with a device enabling the simultaneous remote triggering of eachalarm unit for the purpose of checking the operational readiness of thesame.

Alarm units, in their basic structural format, generally comprise anelectrical switch or contact which, upon the occurrence of apredetermined change in magnitude ofsome condition being monitored,alters its switching state. The change or alteration of the switchingstate generally triggers an indicating device at some remote, centrallocation. If the basic alarm unit is of the type wherein its switchingor electrical contact is normally open in the rest or unactuatedcondition of the associated alarm unit, then one would be concerned withthe measurement of a working current in the entire alarm circuit toindicate the occurrence of an alarm condition. On the other hand, if thealarm unit is such that its switching contact nor mally is closed whenits associated alarm unit is in a rest or unactuated condition, then onewould be concerned with detecting the interruption of some ambientcurrent which normally would be flowing from the remote central stationthrough the alarm unit except upon the occurrence of an alarm condition.Alarm units of this basic type can generally be connected either inseries with one another or in parallel circuit relation within any givensignal installation. Generally speaking, if the individual alarm unitsare all connected in series, then such alarm units must be of the typewherein their individual switching contacts are normally closed andwherein the signal installation draws some ambient current during anunactuated condition of the alarm units.

Drawbacks exist when considering this type of an alarm installationwherein each of the alarm units of a plurality of alarm units areconnected in series circuit. For example, upon the occurrence of analarm, an interruption of the normally flowing ambient current throughthe series circuit would occur. The same interruption of the currentthrough the series circuit would also take place upon the occurrence ofsome disturbance, not an alarm, at an alarm unit. Disturbance, asutilized herein, should be construed as a malfunctioning, rather than anactuation, of an alarm unit. Thus, when utilizing a series connection ofa plurality of individual alarm units, disturbances cannot bedifferentiated from an actual alarm condition. When one considers thatpresent day alarm units generally comprise rather complex electroniccircuits which are prone to malfunctions or other disturbances, and whenone further considers that security installations can comprise severalhundred of such alarms wherein the response from each individual alarmunit generally is desired to result in the undertaking of some specificcorrective measure such as would be the case with the utilization ofsuch alarm systems by police or fire departments, then the importance ofbeing able to distinguish between a disturbance and an actual alarm atan individual unit can be better appreciated. By connecting theindividual alarm units in parallel circuit and thus relying on operationwherein the individual contacts of each alarm unit are normally in anopen condition and close upon an alarm condition, higher reliabilitywith respect to the distinguishment of an alarm from a disturbance canbe realized. With a parallel alarm unit connection, a defect or otherdisturbance in one of the alarm units would only cause the particularaffected alarm unit to be placed out of operation and would notautomatically trigger a spurious false alarm at the remote centrallocation. Further when utilizing the parallel connected individual alarmunits, the entire installation is not made inoperative by virtue of asingle defective alarm unit as would be the case when utilizing a seriesconnection of alarm units. This latter drawback has oftentimes precludedthe utilization of series alarm unit connections in modern day alarminstallations.

Continuing with the development of the art, the utilization of signalinstallations comprising a plurality of alarm units, each generallyconnected in parallel with one another across two supply conductorsleading to a central remote location has become more and more prevalent.Provisions normally have been made so as to enable the operator of thesystem to discover and recognize the occurrence of a possible defect ormalfunctioning at one or more of the plurality of alarm units. ln thisregard, so-called checking systems and the like have been developedwhich serve to periodically transmit to each of the alarm unitsalarm-simulating conditions, the response of the alarm units to thealarm-simulating conditions transmitted being monitored at the centralstation. Again, bearing in mind that the type of signal installationreferred to herein comprises a plurality of parallel connected alarmunits having switching contacts which, upon the occurrence of an alarmor an alarmsimulating condition, close to effectively short the supplyconductors, the checking technique proposed in the prior-art involvesthe comparison, at the central station, of the total current l, flowingthrough the alarm units during the checking operation with somereference value current I deviations of the total actual value ofcurrent from the reference value being considered as indicative of adisturbance. Yet, alarm units as actually utilized today are generallynot constructed with very close or high tolerances of their individualelectrical characteristics. Furthermore, the measuring instrumentsgenerally utilized today at the central station to monitor and comparethe difference between the actual current flowing during a checkingoperation and some reference value also are not constructed in a mannerinherently affording a high accuracy of the readings. Thus, thisprior-art. operational-readiness checking technique inherently possessesa high degree of unreliability and, in fact, normally is unsuitable foruse when the system comprises a large number of alarm units, such as 30or more, combined into a single given group. The accuracy of measurementand thus the reliability of the operational-readiness checkingtechniques has been improved in accordance with still another prior-artsystem wherein a separate wire is run from each individual alarm unitback to the central station thus affording the opportunity of monitoringeach alarm unit separately from the others. Yet, this particularapproach is difficult or impossible to be put into practice due to theproblems involved in the installation of the plurality of wires andfurther due to the high economic cost.

SUMMARY OF THE INVENTION Thus, there exists a need in the prior-art forthe provision of a new and improved signal installation of the typeutilizing a plurality of parallel connected alarm units, which signalinstallation, however, enables checking the operational readiness of thealarm units in a particularly simple, economical yet highly reliablemanner. It is the primary object of the instant invention to satisfythis need.

Now, in order to implement the above object as well as further objectsof the instant invention which will become more readily apparent as thedescription proceeds, the invention is generally manifested by thefeatures that, in addition to the usual electrical switching contactscoupled in parallel across the supply conductors in a parallel alarmsystem installation, further electrical contacts are provided at each ofthe tire alarm units and are interconnected in their own seriesconnected circuit. The series connected additional electrical contactsoperate in conjunction with the main or switching electrical contactsyet are coupled in series connection to the central or remote station orlocation with a voltage source and a separate current measuring device.During the checking operation, the current measuring device at thecentral location determines the flow of current through the seriesconnection of additional contacts and, if no such current exits, adisturbance indicating device is triggered.

In effect, then, the provision of the series circuit of additionalelectrical contacts for the checking operation alone affords thesimplicity of operation inherent with the determination of the merepresence or absence of current flow. Yet, the disadvantages of not beingable to distinguish between a disturbance or an actual alarm conditionis eliminated.

BRIEF DESCRIPTION OF THE DRAWINGS The instant invention itself as wellas additional advantageous features thereof will be better understoodfrom the following detailed description of a preferred operationalembodiment, such description referring to the appended drawings wherein:

FIG. I is an electrical block diagram of a preferred embodiment oftheinventive signal installation;

FIG. 2 is a circuit diagram depicting, in simplified form, oneembodiment ol'an individual alarm unit of the system; and,

HG. 2a depicts alternative elements for the circuit of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Describing now the drawings andreferring particularly to the exemplary embodiment of the inventivesignal installation depicted in block circuit diagram in FIG. I, it willbe seen that such inventive installation comprises a plurality of alarmunits 1, l'...electrically connected to a central remote station 2. Forillustrative convenience, however, only two such alarm units 1 and lhave been indicated on FIG. 1 although it should be appreciated that anynumber of alarm units can be utilized. Each of the alarm units 1,l'...are coupled with supply conductors 3 and 4, across such supplyconductors and in parallel circuit relation with respect to one another.Each such alarm units 1, l'...essentially embodies or comprises a signaltransmitter 5, 5...responsive to the occurrence of some condition thatis desired to be monitored. For example, the signal transmitters 5,5'...could be responsive to the size of combustion particles in the airand thus to the occurrence of a fire. Each alarm unit further isprovided with an associated electronic circuit as well as a switch,supply as a relay 6, 6...respectively, actuated by the associated signaltransmitter.

The relay 6 of alarm unit 1 is illustrated as comprising two workcurrent or switching contacts 7 and 8 whereas the relay 6 of alarm unitI is illustrated as comprising a single work current or switchingcontact 7. Contacts 7 and 7' are coupled to the supply conductors 3 and4 in such a manner that, in the closed position of these contacts,supply conductors 3 and 4 are short-circuited. As a further variant ofthe switching contact connection, a relay 37 having a work currentcontact 8' such as illustrated with respect to alarm unit 1' can beconnected in series circuit with the switching contact 7 itself. Ineither case, energization of the relay 6 or 6' effects closing of theadditional contacts 8 and 8', respectively.

The work current or additional contacts 8 and 3' of alarm units 1 and las well as the additional contacts provided in a similar manner for eachof the other alarm units connected in the installation are themselvescoupled in series circuit with one another. The additional contact 8 ofalarm unit I from which the series circuit connection commences isadvantageously coupled with one of the two supply conductors 3 and 4and, in the case illustrated, contact 8 is coupled with supply conductor3. Each of the alarm units 1, l'...further comprises supply conductorinputs 10, l1; l, ll...and exchangeable input and output leads l3 and14, 13', l4...leading to the respective work contacts 8, 8.... Anadditional control input 12, l2'...is provided for each alarm unit andsuch control input as well as its function will be discussedhereinbelow.

The central or remote station 2, which for illustrative clarity andconvenience has been depicted in a simplified form, comprises a battery15 having cells 15a and [b, a signal relay 16, a disturbance indicatorrelay l7, and a testing switch 18 having switch contacts 18a, 18b, and180. The series connection of the battery and the signal relay 16 isdisposed between the clamps or connections 20 and 2! of the supplyconductors 3 and 4. Signal relay I6 is designed in such a fashion thatthe rest" current flowing through the fire alarm groups or units I, ll...when the respective contacts 7, 7...are open does not switch therelay. Upon the occurrence and transmission of an alarm signal by one ofthe alarm units, in other words, upon closing of one of the "work"current contacts 7, 7'....signa| relay I6 responds to the new value ofcurrent flowing in the signal installation and itself closes a workcurrent contact situated between the output terminals or clamps 23 and24 as illustrated. Consequently, an alarm signal indicating lamp 28 istherefore caused to illuminate.

The simultaneous triggering of all of the alarm units for the purpose ofchecking or testing the operational readiness thereof can be undertakenin a number of different ways. For illustrative simplification, theexemplary embodiment of the inventive system depicts each alarm unit ashaving a single control input l2, I2...which is connected to a commoncontrol conductor 9. Control conductor 9 is connected via terminal 22 tothe central station 2 and, via resistor 19, with the center tap of bothcells l5a and lSb of the battery 15. Upon actuation of the testingswitch or key 18, the control conductor 9 is switched via contact 18b tothe input terminal or side of cell l5!) of the battery. By virtue ofthisswitching action, a potential change is caused to appear on the controlconductor 9 and this potential change likewise is reflected at theindividual control inputs I2, l2...ofthc alarm units thus causingtriggering of the alarm units to actuate relays 6, 6...therein assumingthe individual alarm unit is functioning properly.

Obviously, the triggering of the alarm units for the purpose of checkingthe operational readiness of such units, can take place in a variety ofdifferent manners utilizing different techniques. One such techniqueknown to the art utilizes supply conductors 3 and 4 to trigger thechecking operation and thus do not require the provision of anadditional control conductor 9. So as to suppress, during theoperational readiness checking operation, the transmission of an actualalarm signal such as would occur, for example, upon triggering of a firealarm, the signal relay 16 is shunted or bypassed via the action ofcontact [8a which places a small resistor 28 across the relay l6.

The series circuit connection of the additional work current contacts 8,8'...of the individual alarm units is coupled to the battery 15 at thecentral station 2 via a terminal 27 and a disturbance relay l7.Disturbance relay [7 comprises a spe cialized form of a common currentmeasuring device. During an operational readiness checking operation, ifall of the individual alarm units are functioning and operatingproperly, then a current circuit is closed comprising battery 15,resistor 28, switching contact 28a, supply conductor 3, the seriesconnection of the plurality of additional work contacts 8, 8'..., andthe disturbance relay l7. Disturbance relay 17 would then respondopening its associated switching contact in the auxiliary currentcircuit consisting of the terminal 25, a checking switch contact whichis closed by action of switch 18, indicating lamp 29, and the terminal26. Thus, if all of the individual alarm units properly respond to theoperational readiness check, disturbance indicating lamp 29 will notilluminate.

On the other hand, if only a single alarm unit fails to respond duringthe checking operation, then at least one of the additional workcontacts 8, 8'...would fail to close and disturbance relay l7 wouldremain unexcited. Thus, the auxiliary current circuit comprising theterminal 25, the closed checking switch contact 18c, illuminating lamp29, and terminal 26 would remain in a closed, continuous loop path suchthat the disturbance indicating lamp 29 would illuminate.

Although the additional work current contacts 8, 'mutilized for theoperational readiness checking procedure have been described as beingconnected in series circuit and particularly the connection of theterminal 13 comprising the checking input of the first alarm unit ll hasbeen described as being coupled with one of the two supply conductors 3and 4 leading back to the central station 2, it should be appreciatedthat a direct connection with a separate conductor can be made fromterminal I3 of the first alarm unit I back to the central station 2.

Referring now to FIG. 2, a preferred embodiment of an actual alarm unitutilized in the inventive signal installation is disclosed, the alarmunit itself generally being of known construction and being equippedwith ionization chambers or compartments so as to operate as a firealarm. A measuring ionization chamber 30 is disposed in series circuitrelation with a reference ionization chamber 31 across terminals 1] and12 of the signal installation described with reference to FIG. I. Themidpoint between the ionization chambers 30 and 31 is coupled via a leadto an amplifier element having a high ohmic input, the amplifier elementbeing illustrated here as comprising a field-effect transistor 32, thecathode of which is prebiased via a voltage divider resistor 33 andresistor 34, the anode of which is coupled to the base of a furthertransistor 36. A resistor 35 is connected in parallel to theemitter-base path of transistor 36 whereas the emitter of transistor 36is directly coupled to supply conductor II. The collector of transistor36 is coupled to the supply conductor I0 through a relay winding 37.

Now, if the potential at the gate of the field-effect transistor 32undergoes a change such as an increase of the gate-cathode voltage, thenfield-effect transistor 32 and therefore, transistor 36, begins toconduct. The potential change necessary at the gate of field-effecttransistor 32 as described may be brought about by a change in theionization current flowing through the ionization chambers 30 and 3] dueto the occurrence of a fire, or may alternatively be brought about dueto a change of the voltage at the control terminal 12 such as would bethe case during an operational-readiness checking procedure initiated atthe central station 2. in any case, when transistor 36 begins toconduct, a current flows between supply conductors and 11 throughtransistor 36 and the relay winding 37, this current flow triggering thealarm indicating device at the central station and simultaneouslycausing the closing of contact 8 depicted here as a gas-enclosed reedswitch due to the interac tion between the reed switch and the relaycoil 37. Accordingly, transistor 36 assumes the function of relay 6' andits associated work contact 7' such as described with respect to theoverall installation of FIG. I. On the other hand, the additional workcurrent contact 8 described with respect to the alarm unit 1' of FIG. Ifinds its counterpart in the actual alarm of FIG. 2 in the reed switch8. Relay coil 37 of the alarm unit depicted in FIG, 2 serves the samefunction as relay 37 of the signal installation in FIG. 1.

Now, if any type of a malfunction or defect occurs at the alarm unit ofFIG. 2, other than a sticking of the contacts 8, 8'...in a closedposition, such occurrence being highly improbable, then during anoperational-readiness checking procedure initiated at the centralstation, reed contact 8 would remain open. As described with respect tothe installation of FIG. 1, if this would occur, a disturbance would beindicated by the disturbance indicating lamp 29. By virtue of thisarrangement, it is ensured that each element which is essential for thetransmission of an alarm, including transistor 36, is monitored. Asshould be appreciated, a separate monitoring of the supply conductorssuch as would be required with signal installations of the prior-art, isnot necessary with the novel system of the instant invention.

It should also be appreciated that the additional switching elementdescribed herein as the relay 37 and the associated reed switch contact,can be replaced by other suitable components. For example, as shown inFIG. 2a, a light source 40 instead of relay winding 37 could be utilizedin conjunction with a photoelectric cell 42 instead of the mechanicalreed switch contact ll. Alternatively, a temperature-sensitive rexintor44 could be utilized having a heating winding 46. The alternativeprovision of a light source and a photoelectric cell is particularlyadvantageous if the alarm unit itself is previously equipped with sometype of an individual-indicator lamp signifying a proper operation. Ifthis indicator lamp is simultaneously used as the light source for thephotoelectric cell, then, apart from the economies realized by thisphysical construction, proper operation of the indicator lamp is alsosimultaneously monitored. It should further be appreciated that allswitch elements described as comprising relays with associated workingcurrent contacts and the like can be replaced by electronic circuits andcircuit elements such as transistors. Yet, if such replacement weremade, the checking circuitry itself might take on a unidirectionalnature prohibiting the free exchangeability within the checking circuitof the input and outputs l3 and 14, respectively, of the individualalarm units, which cxchangcability, of course, constitutes an advantagefrom the installation standpoint.

It should now be apparent that the objects set forth at the outset ofthis specification have now been successfully achieved. ACCORDINGLY,

lclaim:

l. A signal installation comprising a plurality of alarm units connectedin parallel circuit relation across a pair of supply conductors with acentral station, said alarm units each comprising a main switch elementresponsive to triggering of the associated alarm unit to shunt saidsupply conductors with a signal current circuit; means for thesimultaneous remote triggering of the alarm units for checking theoperational readiness of the same; each of said alarm units comprisingadditional work current switches normally closed in response to saidremote triggering; circuit means connecting said additional work currentswitches of the individual alarm units in series circuit relation and tosaid central station, said circuit means comprising a voltage source anda current measuring means; said current measuring means, during thechecking operation, monitoring the flow of a work current and, upon theabsence of a current flow, triggering a disturbance indicator at saidcentral station.

2. A signal installation as defined in claim I, wherein said additionalwork current switches comprise reed switches in a protective gasatmosphere.

3. A signal installation as defined in claim 2, wherein each of saidreed switches have an associated relay winding, means coupling saidrelay winding for the reed switch of each individual alarm unit inseries circuit with said main switch element of the associated alarmunit, whereby closing of said main switch element in response totriggering of the associated alarm unit effects closing ofsaidassociated reed switch.

4. A signal installation as defined in claim 1, wherein said additionalwork current switches of each alarm unit comprise photoelectric elementsand associated lamp means therefor, said lamp means being operativelyconnected with said main switch element and said signal current circuitof the respective alarm unit.

5. A signal installation as defined in claim 4, wherein said lamp meanscomprises an individual indicator lamp indicating the operationalreadiness ofan alarm unit.

6. A signal installation as defined in claim 1, wherein said circuitmeans providing said series connection of said additional work currentswitches includes one of said supply conductors.

7. A signal installation as defined in claim I, wherein said alarm unitscomprise fire alarms.

